1. Field of the Invention
The present invention relates to an illuminating system designed to eliminate speckles of laser light and a projection TV employing the same, and more particularly, to an illumination system designed to efficiently reduce or eliminate laser speckles by spatially averaging laser beams using a diffractive optical element and a projection TV employing the same.
2. Description of the Related Art
A projection TV using a laser light source unit is capable of providing a wide range of color expression and has a small divergence angle and high optical efficiency due to a superior collimating property, and thus can have a small size. However, in addition to these advantages, projection televisions utilizing laser light sources suffer from speckles of laser light due to the coherency of the laser light. Speckles of laser light are generated due to the interference with an arbitrary phase when coherent beams are reflected from a rough surface. Such speckles of laser light are the main factor in the degradation of the resolution and of the quality of images.
U.S. Pat. No. 6,594,090 discloses a conventional projector that can remove laser speckles.
Referring to FIG. 1, the conventional projector includes a laser light source 20, a beam expanding optical unit 24, a diffuser 34, and a beam shaping optical unit 38, which are coaxially arranged. The beam expanding optical unit 24 includes a diverging lens 26 and a collimating lens 30. The beam shaping optical unit 38 includes a fly's eye integrator 40, a condenser lens 44, and a field lens 46.
The beam expanding optical unit 24 expands beams emitted from the laser light source 20 into collimated beams with larger diameters. The beam shaping optical unit 38 shapes the beams with Gaussian distributions to have uniform intensity distributions by overlapping the expanded beams and adjusts the shapes of the beams to match with the shape of a liquid-crystal spatial light modulator 52. The beam reflected by the liquid-crystal spatial light modulator 52 is reflected by a polarizing beam splitter 50 and is enlarged and projected onto a screen 60 by a projection lens 58, so that an image is displayed on the screen 60.
In the conventional structure, the beams diffused by the diffuser 34 are radiated by the beam shaping optical unit 38 toward the spatial light modulator 52 such that they overlap, thereby eliminating laser speckles. However, eliminating laser speckles only using the diffuser 34 as described above results in low speckle removing efficiency and a degraded image quality.